From e38fd2056a8cab7a3c6f3da8150fed69530bde6c Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Mon, 13 Apr 2026 14:14:08 +0200
Subject: kstd: introduce output buffer for formatting

---
 libs/kstd/include/kstd/bits/format/context.hpp     | 12 ++++-----
 .../include/kstd/bits/format/output_buffer.hpp     | 30 ++++++++++++++++++++++
 2 files changed, 36 insertions(+), 6 deletions(-)
 create mode 100644 libs/kstd/include/kstd/bits/format/output_buffer.hpp

diff --git a/libs/kstd/include/kstd/bits/format/context.hpp b/libs/kstd/include/kstd/bits/format/context.hpp
index 478a48f..e8d0302 100644
--- a/libs/kstd/include/kstd/bits/format/context.hpp
+++ b/libs/kstd/include/kstd/bits/format/context.hpp
@@ -4,6 +4,7 @@
 // IWYU pragma: private, include <kstd/format>
 
 #include "arg.hpp"
+#include "kstd/bits/format/output_buffer.hpp"
 
 #include <kstd/os/error.hpp>
 
@@ -29,11 +30,7 @@ namespace kstd
 
   struct format_context
   {
-    using writer_function = void(void *, std::string_view);
     using format_args = std::span<format_arg const>;
-
-    writer_function * writer{};
-    void * user_data{};
     format_args args{};
 
     [[nodiscard]] auto arg(std::size_t const id) const -> format_arg const &
@@ -47,13 +44,16 @@ namespace kstd
 
     constexpr auto push(std::string_view string) -> void
     {
-      writer(user_data, string);
+      m_buffer->push(string);
     }
 
     constexpr auto push(char character) -> void
     {
-      writer(user_data, std::string_view(&character, 1));
+      m_buffer->push(character);
     }
+
+  private:
+    bits::format::output_buffer * m_buffer;
   };
 
 }  // namespace kstd
diff --git a/libs/kstd/include/kstd/bits/format/output_buffer.hpp b/libs/kstd/include/kstd/bits/format/output_buffer.hpp
new file mode 100644
index 0000000..be2034f
--- /dev/null
+++ b/libs/kstd/include/kstd/bits/format/output_buffer.hpp
@@ -0,0 +1,30 @@
+#ifndef KSTD_BITS_FORMAT_OUTPUT_BUFFER_HPP
+#define KSTD_BITS_FORMAT_OUTPUT_BUFFER_HPP
+
+#include <string_view>
+
+namespace kstd::bits::format
+{
+
+  //! An abstract interface for formatted output buffers.
+  //!
+  //! This interface is intended to be use for functions dealing with string formatting, like the print and the format
+  //! family.
+  struct output_buffer
+  {
+    virtual ~output_buffer() = default;
+
+    //! Push a text segment into the buffer.
+    //!
+    //! @param text The text segment to push.
+    virtual auto push(std::string_view text) -> void = 0;
+
+    //! Push a single character into the buffer.
+    //!
+    //! @param character The character to push into the buffer.
+    virtual auto push(char character) -> void = 0;
+  };
+
+}  // namespace kstd::bits::format
+
+#endif
\ No newline at end of file
-- 
cgit v1.2.3